Carbon resistance and method of producing and adjusting same.



PATENTED MAR. 1, 1904.

G. I. LEONARD. CARBON RESISTANCE AND METHOD OF PRODUCING AND ADJUSTING SAME.

APPLIOATIOI FILED IEB. 3 1903.

N0 IODEL.

Inventor Gearye ZLeonard I5 suchmet od.

- 2 or on 'theapplication'of permanent pressure.

45' by me that the resistance of a coating or layer No. 753,716. Patented March '1, 19o";

GEORGE-I. LEONARD, or PASADENA; CALIFORNIA CARBON RE SISTANQE AND METHOD OF PRODUCING AND ADlUSTlNG SAME.

Patent No. 753,716, dated March 1, 1eo4. Serial No. 141,7, CH0 specimens.)

srncrncurioiz forming part of Letters Application filed I'ebmry 3, 1903.

To all whom itjrtay concern:

.. Be it known thatI, GEORGE I-. LEONARD, a

citizen of the United States, residing at Pasadena, in the-county of Los Angeles and State of California, have invented a new and useful Carbon Resistance and Method of Producing.

and Adjusting Same, of which the following is a specification.

This invention relates to a method of producing and definitely adjusting or regulating a resistance composed of graphite or similar material used in rheostatic devices, such as electric heaters and current-controllers.

The invention also relates to-the product of conductors may be'decreased in proportion to the pressure exerted; but in such cases the. change has generally been temporary, the carbon increasing in resistance as soon as the pressurewas removed. By subjecting the carbon or plumbago layer to a frictional pressure, as by rubbing, it may be permanently lowered in resistance, and my inventionis based on this new discovery.v My invention also includes the product consisting of the insulatingsupport, with the coating thereon compacted and polished by rubbing. I will now describe my newly-invented nying drawings, where1n y Figure I is a diagram showing. apparatus and electrical connections required in carrying out my method. Fig. II-is a vertical sec- Fig; III is a the resistance in itsfinal- One object of the invention is to provide a method of influencing and controlling the resistance of such material which shall not depend jon\ the addition or removal of material tion'of the resistance element.

vertical section of ondition.

The resistance porting or core In the manufacture of; resistance elements "for rheostats it is found convenient to apply a coating-or layer of plumbago to' one or both sides of a suitable insulating supporting sheet or plate, and for such application the plumbago must be mixed with 'a suitable .binder. As such mixture has a resistance very differ ent' from the plumbagoinits eventual dried condition, it is evidently impracticable to pro- 3 duce accurately adefinite resistance by the simple application of the coating.

An object of my invention is therefore to subject the. coatingfwhenit is in or nearly'in its final dried condition to a treatment that will accurately adjust and permanently fix its element 1 comprises asup plate or sheet 1, with coatnal strips 1 of metalat the ends-J 2 2 indicate terminal clamps connected'by binding-posts 3 3.withan electric circuit 6,; which includes a battery i and ammeter 5. or similar insulating refractory material, is coated, preferably from end faces, with plumbago or carbon 1, the thickness of each coating being made so slight that without the subsequent treatment the resistance would be higher than required. The

resistance according to a (hater-mined standard. plumbago is desirably applied in the state of a- 4 Another object of my invention is to renpaint or paste with water and suflicient sugar der the coating of greater conductivity, so that or similar biinder to cause it to adhere to the a smalleramount of coating material will sufsupport, an it may be applied with aibrush or similar means.

4 fice to carry the current. This not only re-.

ing 1s dry or nearly sults in economy of material, but the coating being thinner than would otherwise be necessary it is less liable to flake ofl.

My invention is based on th discovery made so it is ready for treatment accordingto my method tocontrol or adjust its resistance. The terminal strips first having been fastened on thefends of the resist- I ance element, the latter is connected,by means. of terminals 2 2 in the electrical circuit 6, with the battery and ammeter 5, as shown, an the deflection of the conductivity or conductance of the resistance of plumbago or carbon may be lowered to a considerable extent by t application of fllqtional pressure. By the application of ordinary static pressure the resistance of carbon ings '1 on each side thereof and with termito end on both method, reference being had to the accompa- A sheetor core plate 1,-desirably of asbestos After the plumbago coat-. 1

ammeter will show the element, which for the purpose of adjustment, as above stated, will be considerably lower than required in the final product. Then by means of any suitable implement-such as the brush 7 (indicated in the drawings) or a scraper or roller or any object which will produce a requisite polishing and compacting effect-the coating of plumbago is subjected to frictional or rubbing pressure, and thereby measurably compacted and polished, which effects an increase in the conductivity of the coating, as will be indicated by the increased deflection of the ammeter. If the supportingsheetis coated on both sides, it is desirable to rub one side only enough to bring the conductivity part way up to the required amount, the resistance element being then inverted and the other side rubbed until the resistance is lowered to the required standard, as shown by the ammeter. The resistance element may then be removed from the clamps 3 3 and in serted in a rheostat, and it will be found that the increased conductivity imparted to it will be substantially permanent. The process therefore affords a means of accurately controlling the resistance of the rheostat element, as the rubbing may be stopped just as soon as the ammeter shows that the proper resistance has been reached. lnasmuch as the coating or coatings will be much thinner than if they are simply laid on wet and then dried and used without my special treatment, it follows that less plumbago willsufice, and the coating will adhere more strongly and be less apt to flake off. Moreover, the heat generated in the coating will be more readily conducted away and thrown ofi, as the layer I it has to pass through is thinner and also a better conductor of heat.

It may be assumed that the increased conductivity of the carbon is due to arearrangement of the particles under the frictional pressure, they being caused to lie in closer arrangement and contact. As stated, mere pressure does not produce any such result, it appearing that the disturbance or shifting of the particles is'necessary to their arrangement in closer or more compact order; nor is any considerable pressure necessary when the frictional feature is present, as will appear from the fact that anordinary brushpressure is sufiicient.

My invention is not necessarily limited in its application'to plumbago, but may be applied to any carbon resistance material and generally to any material that presents the necessary features of a fine state of division and of a conductivity depending on closeness of contact; nor do I confine myself to measuring the resistance in the manner herein I dry coating to frictional in passing specified, as it may be measured in any similar manner.

What I claim, and desire to secure by Letters Patent of the United States, is-

1. The method of adjusting the resistance of graphite or similar material which consists in -su jecting same to a frictional pressure until the resistance is reduced to the required amount.

2. The method of adjusting the resistance of a carbon layer which consists in subjecting the layer to 'frictional pressure until the resistance is reduced to the required amount.

3. The method of controlling the resistance of a carbon rheostatic materialwhich consists in subjecting the same to frictional pressure.

4;. The method of producing a carbon rheostat of definite resistance which consists in coating a suitable surface with plumbago and subjecting the coating to frictional pressure.

5. The method of producinga carbon rheostat of definite resistance which consists in coating a suitable support with paste or paint, allowing same to dry and subjecting the dry or nearly dry coating to frictional pressure.

6. The method of producing a carbon rheostat of definite resistance which consists in coating a suitable non-conducting support with a paint or paste composed of plumbago, water and a binding agent, allowing the coating to dry and subjecting the dry or nearly or rubbing pressure until the required resistance is obtained.

7. The method of adjusting the resistance of a carbon rheostatic device which consists in measuring the resistance of said device, and while continuing to measure the resistance, subjecting the carbon in the rheostatic device to frictional pressure until the resistance is reduced to the required amount.

8. The method of adjusting the resistance of a carbon rheostatic device which consists an electric current through said device, and measuring by means of said current the resistance of said device, and while continuing to so apply the current and measure the resistance, subjectingthe carbon in" the rheostatic device to frictional pressure until the resistance is reduced to the required amount.

In testimony whereof I have signed my name to this specification, in the presence of two subscribing witnesses, at Los Angeles, in the County of Los Angeles and State of California, this 19th day of January, 1903.

. GEORGE I. LEONARD. Witnesses:

FREDERICK D. LYoN, JULIA TOWNSEND.

pl umbago 

